JP2005180962A - Electromagnetic flow rate sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fluctuation of the sensitivity of a sensor by the adsorption and precipitation of a metal such as copper on the wetted part of metal shell made of stainless steel 304. <P>SOLUTION: The sensor 3 is fixed to a piping 1 by screwing a fixing nut 12 together with a socket 2 welded to the piping 1, and the tip of the sensor 3 shown as a right end in the figure is inserted into the liquid 10. The male screw 4c of the metal shell 4 is screwed together with the female screw of the insulation sleeve 13, and the outer male screw of the insulation sleeve 13 is screwed together with the female screw of the fixing nut 12. Thereby, the metal shell 4 is fixed to the fixing nut 12 through the insulation sleeve 13. Because, the piping 1 and the socket 2 are insulated from the metal shell 4 of the sensor 3, the metal such as copper never precipitated on the surface of the metal shell 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement of an insertion type electromagnetic flow rate sensor.

  In order to measure the flow rate of liquid flowing in a pipe, an insertion type electromagnetic flow velocity sensor using the principle of electromagnetic induction is well known, and a small sensor with a fixed size can be used regardless of the diameter of the pipe. Since the flow velocity of fluid (liquid) can be detected by inserting it into the pipe, there is an advantage that it is easy to install and the cost is relatively low. In recent years, the use tends to expand.

  This type of electromagnetic flow velocity sensor is used by inserting the tip of the sensor into a conduit through which the fluid to be measured flows. The outer peripheral portion of the front end of the sensor is formed of a metal cylindrical portion (metal shell), and this metal shell is in contact with the fluid to be grounded (see, for example, Patent Document 1).

  FIG. 1 is a longitudinal sectional view for explaining the measurement principle of an electromagnetic flow rate sensor. A tip of an electromagnetic flow rate sensor 3 including a cylindrical metal shell 4 with an electromagnetic flow rate sensor 3 attached to a socket 2 welded and fixed to a pipe 1. The portion (the right end portion in the drawing) is inserted and installed in the pipe 1. Reference numeral 5 denotes a body made of an electrically insulating material such as a synthetic resin, and has two electrodes 6 and 6 at its tip (right end in the figure). 7 is a core, 8 is a yoke, and 9 is an exciting coil wound around the core 7. When an exciting current is applied, a magnetic flux Φ corresponding to the direction of the current is generated in the fluid. When the fluid flows in a direction perpendicular to the paper surface, an induced voltage proportional to the flow velocity is generated between the electrodes 6 and 6, and is amplified by a preamplifier (not shown).

  The front end portion (right end portion in the figure) of the metal shell 4 is connected to the fluid that is the fluid to be measured and is set to the ground potential. The metal shell 4 is often made of stainless steel due to demands for strength, corrosion resistance, and potential stability as ground.

  In piping for mounting an electromagnetic flow rate sensor, for example, hot water piping in an air conditioning system of a building, a galvanized pipe (SGP pipe) galvanized on iron is often used. Since the hot water piping for air conditioning passes through the heat exchanger using a copper tube, copper ions are dissolved in the hot water. Copper is adsorbed and folded out in the manner of electroplating in the liquid contact portion of the metal shell 4 in FIG. This will be described below with reference to the schematic diagram of FIG.

  In the figure, the pipe 1 is galvanized on the surface of the iron pipe 1a as indicated by reference numeral 1b. Further, the socket 2 welded to the pipe 1 is galvanized 2b on the surface of the iron 2a. The sensor 3 is attached and fixed to the socket 2 by screwing the male thread portion of the electromagnetic flow rate sensor 3 into the socket 2. Thus, the male screw portion of the sensor 3 is electrically connected to the socket 2 and the pipe 1 via the female screw of the socket 2, and the metal shell 4 at the tip of the sensor 3 is also electrically connected to the socket 2 and the pipe 1. It will be.

When the zinc plating 1b on the surface of the pipe 1 and the zinc plating 2b of the socket 2 are dissolved as zinc ions Zn ²⁺ in the hot water 10 flowing in the pipe 1 as shown by the arrow A, the zinc plating 1b and 2b portions Negative charges (electrons) move to the sensor 3 side as indicated by an arrow B and gather near the surface of the metal shell 4 that is electrically connected. This negative charge is denoted by reference numeral 11. As described above, since the copper ions are dissolved in the hot water 10, the copper ions are adsorbed by the negative charges 11 of the metal shell 4, and copper is folded out on the surface of the metal shell 4. This phenomenon is the same as when the surface of the metal shell 4 is plated with copper.

The liquid (for example, hot water 10) flowing through the pipe 1 is not limited to the copper ions, and other metal ions may be dissolved, and these are made of stainless steel that is electrochemically noble with respect to zinc. Adsorbed on the surface of the metal shell 4, the metal breaks out in the same manner as in the case of copper. In FIG. 2, the metal ions in the fluid are indicated by the symbol M ⁺ including the copper ions.

  By the way, as an example of the order of the ionization tendency of metals, the corrosion potential sequence in seawater is as shown in Table 1 (for example, see Non-Patent Document 1). Table 1 shows the electrode potential [v] when collating the saturated calomel electrode.

  When the metal touches water, the potential of stainless steel is relatively high as shown in Table 1, and the potential decreases in the order of copper, aluminum, and zinc. When the different potentials in Table 1 are electrically connected, the metal with the lower potential (that is, the electrical base) melts, and the resulting electrons are transformed into the higher potential metals in the table ( Gathered electrically).

In this state, when a metal having an intermediate potential between the connected metals is dissolved in the fluid, that is, in the case of FIG. 2, a metal such as copper or aluminum having a potential between zinc and stainless steel 304 is in the fluid. When melted, copper or aluminum is adsorbed and folded on the outer periphery of the electrically precious metal in which electrons are collected, in this case, the metal shell 4 (stainless steel 304 material) at the tip of the sensor 3.
Japanese Patent Laying-Open No. 2003-194842 (page 3, FIG. 3) Hidetoshi Fukuzawa, “Principles of Galvanic Corrosion and Prevention Measures” Nakagawa Corrosion Industry Co., Ltd., Technical Number 357, September 1990, P4

  Some air conditioners use copper pipes for the coils of heat exchangers through which hot and cold water flow. Therefore, when an electromagnetic flow velocity sensor with a stainless steel metal shell is attached to a galvanized pipe, the pipe and the metal shell of the sensor are electrically connected, and copper or the like is contained in the fluid (hot water or cold water). As the metal melts, these metals adsorb and fold out on the wetted surface of an electrically precious stainless steel metal shell, resulting in a change in the earth impedance seen from the sensor electrode, resulting in an electromagnetic flow velocity. There was a problem that the sensitivity of the sensor would change.

  When hot water was actually flowed through the galvanized piping, when the copper pipe was used for the coil of the heat exchanger, it was confirmed that the sensitivity of the electromagnetic flow rate sensor decreased by about 10% in a short period of several days. . At this time, copper broke out at the liquid contact portion of the metal shell at the tip of the sensor and was oxidized black.

  Therefore, an object of the present invention is to provide an insertion type electromagnetic flow rate sensor that can solve the above-mentioned problems by preventing such adsorption and folding of the metal.

  The main feature of the present invention is that the metal shell of the sensor is basically electrically insulated from the fluid piping in order to prevent dissimilar metals from folding out at the wetted part of the stainless steel metal shell of the electromagnetic flow rate sensor. And

According to the first aspect of the present invention, the outer periphery of the tip of the sensor is formed of a cylindrical metal shell, and at least the tip of the metal shell comes into contact with the pipe when the sensor is inserted into a pipe through which the fluid to be measured flows. In the electromagnetic flow rate sensor,
An electromagnetic flow velocity sensor comprising an insulating means for electrically insulating a pipe and a metal shell.

  According to a second aspect of the present invention, in the electromagnetic flowmeter of the first aspect, the insulating means is an insulating sleeve attached to the inner periphery of a mounting bracket for screwing the sensor onto the pipe.

  According to a third aspect of the present invention, in the electromagnetic flowmeter according to the second aspect, the insulating sleeve is screwed onto the inner periphery of the mounting bracket.

  According to a fourth aspect of the present invention, in the electromagnetic flowmeter of the second aspect, the insulating sleeve is formed by outsert molding inside the mounting bracket.

  According to a fifth aspect of the present invention, in the electromagnetic flow meter of the first aspect, the mounting bracket for screwing the sensor into the pipe is divided into two in the axial direction, both are electrically insulated and fixed, and the front end side of the sensor One of the two positions is provided with a male screw for screwing into a pipe, and the other is provided with a female screw that is screwed into a metal shell.

  Even if the galvanizing of the pipe is melted, the pipe and the metal shell are electrically insulated, so that electrons are not collected from the pipe into the metal shell. Therefore, even if metal ions such as copper are present in a liquid (fluid) such as hot water or cold water, these metals are not adsorbed by the metal shell of the sensor and folded. As a result, the sensitivity change of the sensor can be prevented.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  The embodiment shown in FIG. 3 is a preferred embodiment of the present invention. A socket 2 welded to the pipe 1 is provided with a female screw 2c. The mounting bracket 12 has a tapered male screw 12a at the right end in the drawing, that is, at the tip end. In the electromagnetic flow rate sensor 3, a body 5 made of an electrically insulating material is disposed and fixed inside a substantially cylindrical metal shell 4 made of stainless steel 304, as in FIG. 5 slightly protrudes into the fluid (for example, hot water) 10.

  The mounting bracket 12 has a hexagonal outer shape similar to the prior art of FIG. 2, and a tool is fitted into the hexagonal portion, and the taper male screw 12 a is screwed into the female screw 2 c of the socket 2, so that the sensor 3 is attached to the pipe 1. To do. The minimum diameter of the inner diameter of the mounting bracket 12 is a portion indicated by reference numeral 12b, and the small diameter portion of the outer diameter of the metal shell 4 is set slightly smaller than this minimum diameter. Therefore, a cylindrical space (gap) is formed between the outer diameter small diameter portion 4 b of the metal shell 4 and the minimum diameter 12 b of the inner diameter of the mounting bracket 12. Reference numeral 13 denotes a sleeve made of a synthetic resin material as an electrical insulating means. The entire sleeve is substantially cylindrical, and a male screw portion engraved on the outer periphery thereof is tightly screwed to a female screw engraved on the inner periphery of the mounting bracket 12. The sleeve 13 is fixed to the mounting bracket 12. Then, the male screw 4c engraved on the large diameter portion of the metal shell 4 is screwed into the female screw 13c engraved on the inner periphery of the sleeve 13, and the rotational angle position thereof is adjusted, so that the electrodes 6 and 6 are shown in the drawing. The sensor head 14 is rotated so that the predetermined position, that is, the vertical position of the electrodes 6 and 6 and the horizontal position of the electrodes 6 and 6 are inserted at predetermined positions in the pipe, And the angular position around the axis of the metal shell 4 of the sensor (the horizontal axis in the figure). When the predetermined position is reached, relative rotation between the sleeve 13 and the metal shell 4 is stopped by a set screw (not shown), and the angular position between the sleeve 13 and the metal shell 4 is fixed.

  The sensor head 14 houses a preamplifier for amplifying the signal voltage induced between the electrodes 6 and 6 and an electronic circuit for converting the flow velocity signal corresponding to the flow velocity into a telegram and sending it out via the cord 15. Has been. Reference numeral 16 denotes an O-ring provided between the metal shell 4 and the mounting bracket 12 in order to maintain watertightness.

  This embodiment differs from the first embodiment of FIG. 3 only in the mounting bracket 12 and the sleeve 13 of the sensor 3. Therefore, in Example 2, only the mounting bracket 12 and the sleeve 13 are shown in FIG. This embodiment is different from the embodiment in that the insulating sleeve 13 is formed on the circumference of the mounting bracket 12 by outsert molding. Reference numeral 17 denotes an O-ring groove. An O-ring 16 as shown in FIG. 3 is attached to this groove.

  In this embodiment, as shown in FIG. 5, the mounting bracket is divided into left and right parts, male screws 12a are engraved on the first mounting bracket 12A on the right side of the figure, and female screws 13c are mounted on the second mounting bracket 12B on the left side of the figure. Engraved. An insulating plate 18 is interposed between the mounting brackets 12A and 13A, and both the mounting brackets are fixed by screws 20 and 20. Since the insulating collars 19 and 19 are respectively fitted to the screws 20 and 20, respectively. The second mounting bracket 12B is electrically insulated from the first mounting bracket 12A. Therefore, as a result, the metal shell 4 that is screwed into the female screw 13 c is electrically insulated from the pipe 1.

The longitudinal cross-sectional schematic diagram explaining the measurement principle of an electromagnetic flow velocity sensor. The schematic diagram for demonstrating the problem of a prior art. 1 is a partial longitudinal sectional view of Embodiment 1 of the present invention. The longitudinal cross-sectional view which shows the principal part of Example 2 of this invention. The longitudinal cross-sectional view which shows the principal part of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piping 1a Iron pipe 1b Zinc plating 2 Socket 2a Iron 2b Zinc plating 3 Electromagnetic flow sensor 4 Metal shell 4c Male screw 5 Body 6 Electrode 7 Core 8 Yoke 9 Excitation coil 10 Fluid (hot water)
12 mounting bracket 12A first mounting bracket 12B second mounting bracket 12a male screw 13 insulating sleeve (sleeve)
13c Female thread

Claims (5)

In the electromagnetic flow velocity sensor in which the outer periphery of the tip of the sensor is formed of a cylindrical metal shell, and at least the tip of the metal shell is in contact with the pipe when the sensor is inserted and attached to a pipe through which the fluid to be measured flows.
An electromagnetic flow rate sensor comprising an insulating means for electrically insulating a pipe and a metal shell.   2. The electromagnetic flow rate sensor according to claim 1, wherein the insulating means is an insulating sleeve attached to an inner periphery of a mounting bracket for screwing the sensor to the pipe.   3. The electromagnetic flow velocity sensor according to claim 2, wherein the insulating sleeve is screwed to the inner periphery of the mounting bracket.   3. The electromagnetic flow velocity sensor according to claim 2, wherein the insulating sleeve is formed by outsert molding inside the mounting bracket.   The mounting bracket for screwing the sensor to the pipe is divided into two in the axial direction, and both are electrically insulated and fixed, and a male screw for screwing to the pipe is provided on one side located on the tip side of the sensor, and the other 2. The electromagnetic flow velocity sensor according to claim 1, further comprising a female screw threadedly engaged with the metal shell.

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